Various types of work machines may include one or more hydraulic cylinders for aiding in accomplishing a work function. These hydraulic cylinders are configured such that controlled flow of hydraulic fluid into one or more fluid reservoirs in the cylinder has the effect of retracting or extending a piston into or out of the cylinder. The movement of the piston may be used to move various work implements on the work machine. Hydraulic cylinders may be included on nearly any type of work machine such as, for example, track type tractors, wheeled tractors, shovel/excavators, dump trucks, garbage collection trucks, skid steers, etc.
For several reasons, it may be desirable to determine the position of the piston during operation of a hydraulic cylinder. For example, because the piston position may be operatively connected to a work implement, knowledge of the piston position may translate into knowledge of the position, orientation, or state of the work implement. This information may be used for setting motion limits on the work implement or for automating one or more functions of the work implement. Further, knowing the position of the piston in the cylinder may aid in controlling the operating conditions of the cylinder. For example, the operation of the cylinder may be smoothed by slowing the movement of the piston near its fully retracted or fully extended positions.
Several systems have been proposed for determining the position of a piston in a hydraulic cylinder. Many of these systems rely on information provided by one or more sensors associated with a hydraulic cylinder. For example, certain systems may include a position sensor to directly measure the position of the piston. Other systems predict the position of the piston based on information provided by pressure sensors that measure the pressure of the actuating hydraulic fluid in the cylinder. While these systems may be adequate for determining piston position, the addition of sensors can add significant cost and design complexity to the work machine.
Other systems have been contemplated that do not rely on the use of position and/or pressure sensors to determine the position of a piston in a hydraulic cylinder. For example, U.S. Pat. No. 5,004,264 to Kazaki et al. (“the '264 patent”), which issued on Apr. 2, 1991, describes a hydraulic system, used in an automotive suspension system, that includes a position control device to control the position of a piston in a hydraulic cylinder. The position control device functions by monitoring the magnitude of a control signal provided to a solenoid-operated fluid flow control valve. Using a predetermined relationship between the current of the control signal and flow rate in the hydraulic cylinder, the position control device calculates the position of the piston based on the magnitude of the current of the control signal and the period of time during which the current is supplied to the solenoid-operated valve.
While the system of the '264 patent may be able to determine the position of a piston in a hydraulic cylinder without the use of position and/or pressure sensors, the system of the '264 patent includes several shortcomings. For example, while the system of the '264 patent accounts for position prediction errors that can accumulate during operation of the hydraulic cylinder, the system uses this error information only to adjust the final position of the piston. The system of the '264 patent does not make use of this error information to adaptively adjust a position prediction algorithm. Thus, the system of the '264 patent is unable to dynamically model the performance of the positioning system to reduce or eliminate errors from the position calculation.
The present disclosure is directed to overcoming one or more of the problems of the prior art position control system.